JPH05264308A - Electromagnetic flowmeter - Google Patents

Abstract

PURPOSE:To easily detect the empty state of a measuring pipe. CONSTITUTION:By vertically impressing an alternating magnetic field upon a conduit 11 by exciting a coil 17 from an exciting power source 16, a signal electromotive force generated perpendicularly to the magnetic field and the flow of a fluid flowing through the conduit 11 is detected by means of electrodes 12 and 13. A detection circuit 3 which detects excitation noise generated in the signal electromotive force when the direction of the magnetic field is switched at the time of measuring the flow speed or flow rate of the fluid by processing the detecting signals of the electrodes 12 and 13 by means of a processing section is provided so that whether the conduit 11 is filled up with the fluid or no fluid flows through the conduit 11 can be easily discriminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic flowmeter capable of discriminating an empty state where there is no fluid in a measuring pipe or conduit.

[0002]

2. Description of the Related Art FIG. 6 shows the structure of a general electromagnetic flowmeter. That is, the electromagnetic flowmeter is composed of the flow rate detection unit 1, the processing unit (C
The flow rate detection unit 1 includes a conduit 11, electrodes 12, 13, an amplifier 14, an A / D (analog / digital) converter 15, and a PU unit) 2 and a digital / analog (D / A) converter 4. The excitation power source 16 and the coil 17 are included. In such a configuration, the fluid to be measured flows in the conduit 11 and an alternating magnetic field is applied perpendicularly to the flowing direction of the fluid via the exciting power supply 16 and the coil 17. As a result, an electromotive force is generated between the electrodes 12 and 13, and this electromotive force is excited and synchronously rectified in the amplifier 14. This synchronization is performed by a synchronization signal (SY) given from the CPU unit 2 through the line L. The output of the amplifier 14 is converted into a digital amount by the A / D converter 15 and given to the CPU unit 2. C
The PU unit 2 executes a predetermined process, and outputs the instantaneous flow rate output Q or the integrated output V as a digital amount DO. In addition, the instantaneous output Q or the integrated output V of the flow rate from the CPU unit 2 is converted into an analog amount AO by the D / A converter 4 as necessary and output.

[0003]

However, when the fluid in the conduit is emptied in such an electromagnetic flowmeter, phenomena such as abnormal output fluctuation, output hunting, or output swing-out occur and the output becomes unstable. Therefore, conventionally, when such a state occurs, a worker has to infer that it is in an empty state and confirm the fact, which is troublesome. Further, in a control loop that controls by the output of the flow meter, there is a problem that erroneous control is executed based on the unstable output. Therefore, an object of the present invention is to provide an electromagnetic flow meter which can detect that the fluid in the conduit is empty.

[0004]

In order to solve such a problem, according to the present invention, a pair of signal detections for detecting the signal electromotive force generated perpendicularly to the applied magnetic field and the flow of the fluid flowing in the measuring tube. In an electromagnetic flowmeter including at least an electrode and a processing unit that outputs a signal corresponding to the flow velocity or flow rate of a fluid based on a signal from the signal detection electrode, a signal electromotive force is generated when the direction of the applied magnetic field is switched. Is provided to detect the excitation noise, and it is possible to determine whether the inside of the measuring tube is full or empty without fluid based on the output from the detecting means.

[0005]

By providing an empty detection circuit for detecting whether or not the fluid in the conduit is empty based on the excitation noise, it is possible to easily detect the empty fluid and prevent malfunction in the control system.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the essential parts of an embodiment of the present invention. As is clear from the figure, this embodiment is constructed by adding an empty detection circuit 3 to the conventional example shown in FIG. The sky detection circuit 3 is provided to detect whether the inside of the conduit 11 is full or empty without water. FIG. 2 is an explanatory diagram for explaining the principle of the present invention.
1, the relationship between the coil 17 and the signal line L3 is shown.
FIG. 3 is a waveform diagram for similarly explaining the principle of the present invention. That is, as shown in FIG. 2, by sandwiching the conduit 11 between electromagnets composed of the coil 17 and the core C, a magnetic field is vertically applied to the fluid to be measured as indicated by an arrow H. In order to generate this applied magnetic field, a low-frequency rectangular wave, which will be described later, is mainly used because the zero point is stable. When such a magnetic field is applied, each time the direction of the magnetic field is switched, the magnetic field that crosses the closed circuit consisting of the signal line L3, the electrodes 12 and 13 and the conduction by the fluid shown by the dotted line D changes, so that differential noise is generated. Occur. Also, since the magnetic field that traverses the fluid also changes, an eddy current as indicated by arrow I is generated in the fluid.

Due to the influence of the differential noise and the eddy current, the output signal waveform of the amplifier 14 shown in FIG. 1 has a noise waveform (N11 and N12 shown in FIG. 3 synchronized with the switching of magnetic fields even when the fluid is at rest). Hereinafter referred to as excitation noise) is observed. Since this excitation noise corresponds to the changing direction of the magnetic field, (+) and (-) noises are alternately generated. Excitation noise is excitation waveform DR like N11
Whether it goes to the (+) side when rising or when it goes to the (-) side when rising like N12 depends on the delicate positional relationship of the signal line, core, coil, etc. Are different. N21 and N22 indicate noise waveforms corresponding to N11 and N12 when the maximum flow rate flows, and the peak value of this excitation noise generally reaches several times the maximum flow rate. Note that TH1 and TH2 in FIG. 3 indicate threshold values on the (+) side and the (−) side, respectively. More than,
The signal waveform at the time of normal when the pipe is full is shown.

On the other hand, when the conduit is empty, the dotted line D in FIG.
Since there is no conduction by the fluid indicated by, the above-mentioned differential noise does not occur. Further, since there is no fluid, no eddy current is generated, and thus no excitation noise is generated. At this time, since the electrodes 12 and 13 are in an electrically “floating” state, the output of the amplifier 14 has an irregular potential fluctuation,
It will pick up and output electromagnetic noise in the air.
From this, it is possible to know whether or not the inside of the conduit is empty by utilizing the excitation noise generated only when the inside of the conduit is full of water. This is the principle of the present invention.

FIG. 4 is a circuit diagram showing a concrete example of the sky detection circuit. First, the operation during normal time when the inside of the conduit is full will be described. Signal waveforms such as N11 to N22 in FIG. 3 output from the amplifier 14 in FIG. 1 are given to the comparator 30. In the comparator 30, signals such as N11 to N22 sent via the signal line L2 are supplied to the resistor R
1 and R2 are compared with a reference voltage Vt obtained by dividing the voltages V _DD and V _SS, and if the signals N11 to N22 have a higher voltage, the voltage V _SS is output, and if they are lower, the voltage V _DD is output. In addition,
The output voltage of the comparator 30 is fed back to Vt via the resistor R3, and this causes hysteresis.

Now, assuming that the signal voltage is low and the comparator 30 outputs the voltage V _DD , the comparator 3
The reference voltage Vt of 0 is Becomes As shown by TH1 in FIG. 3, when this Vt ⁺ is set higher than the flow rate signal voltage at the maximum flow rate and lower than the (+) peak voltage of the excitation noise N22 in FIG. 3,
The signal voltage is higher than this threshold because
Only when (+) excitation noise occurs. Therefore, the output of the comparator 30 is held at V _DD until the next (+) excitation noise occurs.

When the next (+) excitation noise occurs, the signal voltage exceeds the reference threshold voltage Vt ⁺ , so the output of the comparator 30 becomes V _SS . As a result, the reference threshold voltage Vt is Becomes As shown by TH2 in FIG. 3, this Vt ^- is set to be lower than the flow signal voltage at the maximum flow and higher than the (+) peak voltage of the excitation noise N22 in FIG. 3 (R
By selecting the resistance value of 1, R2, R3, Vt ⁺ , V
t ^- can be set so as to satisfy simultaneously the conditions). This way, (-) signal only voltage Vt when the excitation noise is generated in ^- becomes lower than, then (-)
The output of the comparator 30 is held at V _SS until the excitation noise of 1 occurs.

Next, when (-) excitation noise occurs,
The output of the comparator 30 becomes V _DD , and the threshold voltage changes to Vt ⁺ . Then, the output of the comparator 30 is held at V _DD until the next (+) excitation noise occurs. Thus, the output of the comparator 30 becomes a rectangular wave in which V _DD and V _SS alternate, in synchronization with the excitation noise (that is, in synchronization with the excitation waveform DR).
This rectangular wave has the excitation noises DR and 1 as shown in DE1 of FIG. 3 when the excitation noise appears on the (+) side at the rising edge of the excitation waveform DR like N11 and N21 of FIG.
The waveform has a phase shift of 80 degrees, and when the excitation waveform DR goes to the (+) side at the trailing edge of the excitation waveform DR, such as N12 and N22, the waveform has the same phase as the excitation waveform DR, as indicated by DE2 in FIG.

The output of the comparator 30 is excited and synchronously rectified by an inverter 31 and a rectifying switch 32. That is, in the rectification switch 32, when the excitation waveform DR is on the (+) side by the excitation timing signal TG given from the CPU unit 2 via the signal line L1, the comparator 30
When the output of (1) is on the negative side, the output of the comparator 30 is inverted by the inverter 31 to be selected. As a result, the output signal of the rectification switch 32 has a DC potential of V _SS when the output of the comparator 30 is DE1 and V _DD when it is DE2. R7 and C1 form a smoothing circuit, and its time constant is set to be sufficiently larger than the excitation period, so that high frequencies and ripples in the excitation period are removed.

33 and 34, the output of the rectifying switch 32,
This is a comparator for determining whether or not the DC potential is V _SS or V _DD . The resistors R10 and R13 are also provided with hysteresis respectively for this comparator, but this is for suppressing output hunting, and is set to an appropriate value (about 1 V). The output of the rectifying switch 32 of the comparator 33 is V _DD
It is determined whether or not the threshold voltage is 0V
It is set sufficiently larger and smaller than V _DD . Therefore, if the output of the rectifying switch 32 is larger than this threshold voltage, the output of the comparator 33 is V _SS (L level).
And the output of the NOT circuit 35 becomes H level. On the other hand, in the comparator 34, the output of the rectifying switch 32 is V _SS.
It is determined whether or not the threshold voltage is 0V
It is set sufficiently smaller and larger than V _SS . Therefore, if the output of the rectifying switch 32 is smaller than this threshold voltage, the output of the comparator 34 becomes V _DD (H level). Therefore, the output of the rectifying switch 32 is V
If it is _DD or V _SS , either the comparator 34 or the NOT circuit 35 becomes H level, and therefore the output of the OR circuit 36 becomes H level. As described above, the empty detection circuit 3 sends an H level signal to the CPU unit 2 when the conduit is full of water.

Next, the operation when the inside of the conduit is empty will be described. As described above, excitation noise does not occur in this case. That is, the input to the comparator 30 has a waveform in which an irregularly fluctuating potential or electromagnetic noise in the air is picked up, but when the input voltage happens to exceed the threshold voltage, the output of the comparator 30 changes. Since such a change occurs at irregular intervals, the frequency component that synchronizes with the excitation waveform DR is small, and the output that has passed through the smoothing circuit of R7 and C1 after being synchronously rectified by the inverter 31 and the rectifying switch 32 is 0.
The voltage is close to V. Therefore, the comparator 3
If the absolute values of the threshold voltages of 3 and 34 are made sufficiently large, the output of the comparator 33 becomes H level and the output of the comparator 34 becomes L level. Therefore, the output of the NOT circuit 35 becomes L level, and the output of the OR circuit 36 also becomes L level.
It becomes a level. As described above, when the inside of the conduit is empty, the empty detection circuit 3 sends an L level signal to the CPU unit 2. Therefore, the CPU unit 2 outputs the empty detection circuit 3 so that the inside of the conduit is empty or full. You can judge whether there is.

FIG. 5 shows another embodiment of the sky detection circuit. When the inside of the conduit is full, signal waveforms such as N11 to N22 in FIG.
It is input to 7,38. The threshold voltages of the comparators 37 and 38 are set to the same magnitudes TH1 and TH2 as in the case of FIG. In this way, the comparator 37 outputs V _DD (H level) only when (+) excitation noise is input. Similarly, the comparator 38 outputs V _DD (H level) only when (-) excitation noise is input. The outputs of the comparators 37 and 38 are the SR flip-flop 3
9 and its output becomes L level (V _SS ) when (+) excitation noise occurs, and becomes H level (V _DD ) when (−) excitation noise occurs, and the waveform DE1, FIG.
Matches DE2. This output is used as the comparator 30 of FIG.
If the same process is performed by using the output of the above, the H level output is obtained from the OR circuit 36 as in the case described above. When the inside of the conduit is empty, similarly to the above, when the input signal happens to exceed the threshold voltage, the output of the SR flip-flop 39 switches, and the OR circuit 36 obtains an L level output.

[0017]

According to the present invention, since the empty detection circuit is provided, it is possible to judge whether the inside of the conduit is empty or full. This makes it possible to prevent malfunction of the control system, for example, by issuing an error message from the CPU unit to notify an abnormal state or by setting the output to a predetermined value.

[Brief description of drawings]

FIG. 1 is a configuration diagram of essential parts showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining the principle of the present invention.

FIG. 3 is a waveform diagram for explaining the principle of the present invention.

FIG. 4 is a circuit diagram showing an embodiment of a sky detection circuit.

FIG. 5 is a circuit diagram showing another embodiment of the sky detection circuit.

FIG. 6 is a schematic diagram showing an outline of a general electromagnetic flow meter.

[Explanation of symbols]

1 ... Flow rate detection unit, 2 ... Processing unit (CPU unit), 3 ...
Empty detection circuit, 4 ... D / A converter, 11 ... Measuring tube (conduit), 12, 13 ... Signal detection electrode, 14 ... Amplifier, 15
... A / D converter, 16 ... Excitation power supply, 17 ... Coil, 3
0, 31, 33, 34, 37, 38 ... Comparator, 3
2 ... Rectification switch, 35 ... NOT circuit, 36 ... OR circuit, 39 ... SR flip-flop.

Claims (1)

[Claims] 1. A signal electromotive force generated perpendicularly to an applied magnetic field and a flow of a fluid flowing in a measuring tube is detected.
In an electromagnetic flowmeter comprising at least a pair of signal detection electrodes and a processing unit for outputting a signal corresponding to a flow velocity or a flow rate of a fluid based on a signal from the signal detection electrodes, a signal when switching the direction of the applied magnetic field A detecting means for detecting an excitation noise generated in the electromotive force is provided, and it is possible to determine whether the inside of the measuring tube is full or empty without fluid based on the output from the detecting means. Electromagnetic flow meter.